I think the Titan is still made of steel..right? If so you could use a magnet mount antenna on the roof (I know but it won't hurt the paint if you get a good one) and then route the coax into the cab via the rear brake light. You can create a small pass through for the coax with a rat tail file and then seal it with silicone. When you got to sell the truck, you can remove the antenna and replace the bed light gasket/housing and you're done. Just an idea to consider. I know you said no magnetic mounts, but they can actually be decently good in some circumstances.
Alternatively, they make hood mounts that are adjustable and or you could get one for another vehicle that's close and tweak it to work. The lip mount is used on Jeeps a lot with some success. If you're goal is to be able to use it vehicle to vehicle for a few miles or around town with a base, then that should get the job done.
If you are planning to keep the truck for some time, then you really might want to consider a properly installed NMO mount on the roof. I know the idea of drilling a hole sounds horrid, but in reality, it's not that bad. I have put NMO mounts on the roof of my vehicles for the last thirty years and never regretted it. I use good quality mounts, carefully determine the location and drill away. Once it's on its super solid and waterproof. When I take the antenna off, I put on an NMO rain cap, and the mount just disappears. Heck, these days almost every car has a GPS antenna or something on the roof anyway and no one notices. I have sold or traded in about six cars over the last thirty years and every single one had an NMO mount. Not once did the dealer ever comment on it.
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